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Video Conversion

3. A Conversion Table for Digital Video Formats

The following is a frame size and aspect ratio conversion table, representing many commonly used digital video formats:

The formats related to 625-line systems with a 50 Hz field rate
sampling matrix sampling
rate (MHz)
pixel aspect
ratio (x/y)
sampling matrix width in µs actual active picture size supports
interlacing
notes
width height width height
768 576 14.75 768/767 52.06780 767 576 Y "Industry standard" 625/50 square-pixel video
768 576 14 + 10/13² 1/1 52.00000 768 576 Y "True" computer square-pixel resolution
768 560 14.75 768/767 52.06780 767 576 Y CD-i³
720 576 13.5 128/117 53.33333 702 576 Y D1, DV, DVB, DVD, SVCD³
720 540 ambiguous 1/1 ambiguous 720 540 N Oddball compromise format. Better to avoid unless you really know what you are doing.
704 576 13.5 128/117 52.14815 702 576 Y DVD, H.263 (4CIF), VCD³
702 576 13.5 128/117 52.00000 702 576 Y Active picture frame for 625/50 systems in ITU-R BT.601-4 pixels.
544 576 10.125 512/351 53.72840 526+1/2 576 Y DVB (3/4 of BT.601 sampling rate)
480 576 9 128/78 53.33333 468 576 Y SVCD (2/3 of BT.601 sampling rate)
384 288 7.375 768/767 52.06780 383+1/2 288 N 1/4 of "industry standard" 768×576
384 280 7.375 768/767 52.06780 383+1/2 288 N CD-i
352 576 6.75 256/117 52.14815 351 576 Y DVD
352 288 6.75 128/117 52.14815 351 288 N VCD, DVD, H.261 + H.263 (CIF)
176 144 3.375 128/117 52.14815 175+1/2 144 N H.261 + H.263 (QCIF)
The formats related to 525-line systems with a 59.94¹ Hz field rate
sampling matrix sampling
rate (MHz)
pixel aspect
ratio (x/y)
sampling matrix width in µs actual active picture size supports
interlacing
notes
width height width height
720 540 ambiguous 1/1 ambiguous 720 540 N Oddball compromise format. Better to avoid unless you really know what you are doing.
720 486 13.5 4320/4739 53.33333 710.85 486 Y D1
720 480 13.5 4320/4739 53.33333 710.85 486 Y DV, DVB, DVD, SVCD³
711 486 13.5 4320/4739 52.66667 710.85 486 Y Active picture frame for 525/59.94 systems in ITU-R BT.601-4 pixels.
704 486 13.5 4320/4739 52.14815 710.85 486 Y  
704 480 13.5 4320/4739 52.14815 710.85 486 Y ATSC, DVD, VCD³
648 486 12 + 1452/4739² 1/1 52.65556 648 486 Y "True" computer square-pixel resolution (all 486 active scanlines)
640 480 12 + 3/11 4752/4739 52.14815 646+5/22 486 Y D2: "industry standard" 525/59.94 square-pixel video
640 480 12 + 1452/4739² 1/1 52.00549 648 486 Y "True" computer square-pixel format (cropped)
480 480 9 6480/4739 53.33333 473.9 486 Y SVCD (2/3 of BT.601 sampling rate)
352 480 6.75 8640/4739 52.14815 355.425 486 Y DVD
352 240 6.75 4320/4739 52.14815 355.425 243 N VCD, DVD
320 240 6 + 3/22 4572/4739 52.14815 324 243 N 1/4 of 640×480
¹ 59.94 Hz is only a conventional approximation; the mathematically exact field rate is 60 Hz * 1000/1001.
² A calculated sampling rate, represented here only for completeness. Does not exist in actual 525/625 video equipment.
³ Only used for still images.

3.1 How to use the table for conversions

Let's assume you have a video clip in one format and wish to convert it to another, so that it remains in correct aspect ratio throughout the process.

  1. Locate your source and target formats in the table.
  2. Calculate the vertical conversion factor by using the following formula: vertical_conversion_factor = target_active_picture_height / source_active_picture_height. (Be sure to use the active picture values from the table, not the sampling matrix size values.)
    • If vertical_conversion_factor is 0.5 and your source material is interlaced, you will probably need to deinterlace before resampling. (I recommend using a special smart deinterlacing algorithm, such as the one found in VirtualDub's Smart Deinterlacer filter.)
    • If vertical_conversion_factor is anything other than 0.5, 1 or 2, you are probably trying to do a standards conversion between a 625/50 system and a 525/59.94 system. Standards conversion (when done right) is a highly demanding process and outside the scope of this document. I recommend reading The Engineer's Guide to Standards Conversion and The Engineers Guide to Motion Compensation from Snell & Wilcox Engineering Guides to get a grasp of the related issues. In short, merely converting the frame size and image aspect ratio is not enough - you would also have to take interlacing into account and correct any aliasing problems in temporal dimension (which means synthesizing new fields out of thin air using motion compensation algorithms.)
  3. Calculate the horizontal conversion factor: horizontal_conversion_factor = (source_aspect_ratio) / (destination_aspect_ratio) * (vertical_conversion_factor)
  4. Calculate the new horizontal size: target_sampling_matrix_width = horizontal_conversion_factor * source_sampling_matrix_width
  5. Calculate the new vertical size: target_sampling_matrix_height = vertical_conversion_factor * source_sampling_matrix_height
  6. Resample the image to the new size
  7. Check if the new size matches the target resolution's sampling matrix dimensions. If not, crop (i.e. cut at the edges) and pad (i.e., add black borders) accordingly so that it will.

3.2 Some practical examples of the above

3.2.1 640×480 "industry standard" square pixels to 720×480 ITU-R BT.601 pixels

Let's say I have captured a video clip from 525/59.94 source using an old M-JPEG card that only allows sampling in "industry standard" (12 + 3/11 MHz) square pixel format. The resolution of the clip is 640×480. Now I would like to incorporate this into a DV project that uses ITU-R BT.601 pixels and a resolution of 720×480.

  1. The first step is to look up the correct source and target formats from the table.
    • In this case, the source format is 640×480 in a 525/59.94 system, using the sampling rate of 12 + 3/11 MHz and a pixel aspect ratio of 4752/4739.
    • The target format is 720×480 (likewise in 525/59.94 system), using the sampling rate of 13.5 MHz and a pixel aspect ratio of 4320/4739.
  2. The second step is to calculate the vertical conversion factor. In our case, it is 486/486 = 1
  3. Now we need a horizontal rescaling factor, which in this case is (4752/4739) / (4320/4739) * 1 which equals to 11/10.
  4. Then we can calculate the new image width from the old one: 11/10 * 640 = 704 pixels
  5. The image height will stay unchanged, since 1 * 480 is still 480.
  6. Thus, we need to resample the 640×480 image to 704×480.
  7. However, our original target resolution was 720×480. Now we need to pad the image (with black vertical bars on the side) so that the frame width will become 720 pixels. A natural conclusion is that we need to add 8 pixels black to both side edges.

3.2.2 720×576 ITU-R BT.601 pixels to 720×480 ITU-R BT.601 pixels

In other words, a "PAL" to "NTSC" conversion:

  1. Again, the first step is to look up the correct source and target formats from the table.
    • In this case, the source format is 720×576 in a 625/50 system, using the sampling rate of 13.5 MHz and a pixel aspect ratio of 128/117.
    • The target format is 720×480 in 525/59.94 system, using the sampling rate of 13.5 MHz and a pixel aspect ratio of 4320/4739.
  2. We need to alculate the vertical conversion factor. In our case, it is 486/576 = 27/32
  3. Now we need a horizontal rescaling factor, which in our case is (128/117) / (4320/4739) * (27/32) which equals to 4739/4680.
  4. Then we can calculate the new image width from the old one: 4739/4680 * 720 = 729+1/13 pixels
  5. The new image height will be 27/32 * 576 = 486 pixels.
  6. Thus, we need to resample the 720×576 image to (729+1/13)×486. As we normally cannot use subpixel sampling, we must round the figure 729+1/13 to some reasonable number - in this case probably 729.
  7. However, our original target resolution was 720×480. Now we need to crop the 729×486 image sufficiently from the edges so that the frame width will become 720 pixels and frame height 480 pixels.

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Created: Dec 27, 2015 by
Edited: Dec 27, 2015 by


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